Discharge Nozzle For Molten Metal In Molten Metal Vessel, Method For Operation Of Converter Having The Discharge Nozzle, And Sleeve Replacing Apparatus For Discharge Nozzle Of Molten Metal Vessel

ABSTRACT

An arrangement for reducing an average discharging time in a molten metal vessel, such as a converter, having a molten-metal discharge nozzle particularly a molten-metal discharge nozzle comprises a sleeve-shaped refractory member so as to achieve enhanced operational efficiency of the molten metal vessel. A discharge nozzle comprises an upper sleeve mounted in a refractory lining of a converter and a lower sleeve adapted to be detachably attached to a lower end of the upper sleeve, wherein a hole sectional area of the lower sleeve is set in the range of 60 to 98% of a hole sectional area of the lower sleeve in its used state requiring replacement.

TECHNICAL FIELD

The present invention relates to a discharge nozzle for dischargingmolten metal from a molten metal vessel, such as a converter,particularly a discharge nozzle comprising a replaceable sleeve-shapedrefractory member. The present invention also relates to a method foroperation of a converter having the discharge nozzle, and an apparatusfor replacing the sleeve-shaped refractory member.

BACKGROUND ART

In a refining process for molten metal, such as molten steel,high-temperature molten metal is carried to a refining furnace by atransport vessel, such as a ladle, and transferred from the transportvessel to the refining furnace to refine the molten metal. Then, refinedmolten metal is discharged and returned from the refining furnace to thetransport vessel, and carried to a subsequent work station.

Fundamentally, an operation cycle of the refining furnace consists ofthree steps: a step of receiving molten metal; a step of refining themolten metal; and a step of discharging refined molten metal. In asteelmaking converter as a typical example of the refining furnace, itis required to take about 42.5 minutes as a total operation cycle time,specifically, about 5 minutes for a step of receiving molten steel(charging), about 30 minutes for a step of refining the molten steel(blowing) and about 7.5 minutes for a step of discharging refined moltensteel (tapping).

That is, with respect to the total operation cycle time in thesteelmaking converter, the charging time accounts for about 12%, and thetapping time accounts for about 18%. The charging and tapping, i.e.,receiving and discharging, are a process of simply transferring moltenmetal, and therefore a time to be spent for the molten metal transfer iscommonly called wasted time which has no direct relationship with afundamental function of the converter. Thus, a reduction of a timerequired for the molten metal transfer during the refining process cancontribute to improvement in operational efficiency of a converter toachieve increased annual refining capacity per converter and enhancedproductivity, which leads to reduction in production cost.

Practically, when it is tried to reduce a time required for thereceiving and discharging during the refining process, there are somepoints to be considered in each of the receiving and discharging steps,in addition to developing a technique directly connected to thereduction of receiving and discharging times.

Firstly, in the receiving step of transferring molten metal from atransport vessel to a converter, the transport vessel is tilted to pourthe molten metal into the converter. This pouring operation (e.g.,control of flow volume) has to be accurately managed to prevent damagesin a refractory lining of the converter. Secondly, in the dischargingstep of transferring the molten metal from the converter to thetransport vessel, it is required to prevent a large amount of slaggenerated during the refining step from flowing into the transportvessel. Further, this discharge operation has to be managed to preventthe occurrence of turbulence in a discharged molten metal flow, whichcauses entrainment of ambient air in the discharged molten metal andoxidation of the discharged molten metal due to oxygen contained in theambient air to result in significant quality deterioration.

As above, the requirements in managing the receiving and discharging ofmolten metal during the refining process are different from each other.With a view to facilitating coping with these different managementrequirements, there is a converter having a receiving portion and adischarge nozzle individually. In this type of converter, the dischargenozzle is designed to have a specific inner diameter or opening area soas to minimize outflow of slag therefrom and allow a discharged moltenmetal flow to be formed as close to laminar flow as possible.

Generally, in a converter, an intense flow of high-temperature moltensteel will cause significant chemical/mechanical wear in a tappingnozzle as a discharge nozzle, and a bore of the tapping nozzle will begradually increased. Along with gradual increase in an opening area ofthe tapping nozzle, a discharge flow volume will be increased, andthereby a discharging time, i.e., tapping time, will be reduced.

Then, when the opening area of the tapping nozzle is increased up to agiven value, further intensified flow generates whirls around thetapping nozzle, to entrain slag on a surface of the molten steel in theconverter, and a large amount of entrained slag will be undesirablydischarged to a transport vessel. It is essential to avoid discharging alarge amount of molten steel with entrained slag within a short periodof time, because the slag has adverse effect on quality of steel.

Specifically, it is necessary to set an allowable upper limit to theopening area of the tapping nozzle to be increased every tapping due towear of a refractory member of the tapping nozzle, or set an allowablelower limit to the tapping time based on a relationship between theallowable upper limit of the opening area and the tapping time under thecondition that the opening area is freely increased to reduce thetapping time, and replace the tapping nozzle with a new one when theopening area reaches the allowable upper limit or the tapping timereaches the allowable lower limit, so as to return an inner diameter(i.e., the opening area) of the tapping nozzle to the initial condition.

As typical measures against outflow of slag during tapping, the timingof tilting or rotating of the converter itself is adjusted withoutproviding a valve for blocking the molten steel and slag flow. That is,an actual technique of preventing outflow of slag during tapping isdesigned to tilt or rotate the converter itself in response to detectingentrainment of slag in molten steel flow. Thus, a certain amount of slagis inevitably discharged to a transport converter together with moltenmetal.

An amount of slag to be discharged to the transport vessel isapproximately proportional to the opening area of the tapping nozzle,and further dependent on controllable tilting or rotating speed as oneperformance of the converter. Thus, an amount of slag to be dischargedto the transport vessel can be controlled at a given value or less onlyif the allowable upper limit of the opening area of the tapping nozzleis determined in consideration of the performance of the converter.Further, the allowable upper limit of the opening area of the tappingnozzle for controlling the amount of slag at a given value or less isvaried depending on the performance of the converter.

Generally, it takes long hours to replace a tapping nozzle which has anopening area reaching the allowable upper limit due to wear, and anoperation of the converter has to be interrupted during the replacementto cause lowering in quantity of refining (production).

For this reason, various measures for reducing a time to replace atapping-nozzle have been taken. For example, the following PatentPublication 1 discloses a structure of a tapping nozzle formed with areplaceable sleeve-shaped refractory member, wherein the sleeve-shapedrefractory member is replaced to facilitate reduction in replacementtime of the tapping nozzle. The Patent Publication 1 further discloses atechnique of selecting a highly-durable material excellent in wearresistance to molten metal flow to allow for reducing a frequency ofreplacement of the sleeve-shaped refractory member.

As a technique for speeding up the replacement of such a sleeve, atundish nozzle replacing apparatus designed to push out an old nozzle bya new nozzle has been studied, as disclosed, for example, in thefollowing Patent Publications 2 and 3.

In the above conventional technique of replacing a sleeve-shapedrefractory member, a new sleeve-shaped refractory member is designed tohave a relatively small bore (inner diameter) and a relatively largewall thickness, which correspond to an allowable upper limit of tappingtime (i.e., allowable longest tapping time), so as to provide furtherextended usable life to the sleeve-shaped refractory member itself.Typically, in a converter, a new tapping nozzle is designed to have abore (inner diameter or opening area) which is equal to about one-halfof an upper limit thereof, or which provides a tapping time (i.e.,discharging time) about two times greater than a lower limit thereof.

For example, in a sleeve-shaped refractory member to be used for 200heats (the number of batches of molten steel), while a tapping time isrelatively long, e.g., 10 minutes, in an initial stage of use, it willbe reduced to about 5 minutes in a last stage of use. That is, anaverage tapping time defined by “a sum of respective tapping times inthe entire use period/the number of times of use of the sleeve-shapedrefractory member” is 7.5 minutes.

In this case, given that the shortest tapping time free of entrainmentof slag in a converter is 5 minutes, a tapping time of 2.5 minutes/heatis uselessly spent.

In typical conventional converters, an average time necessary forreplacement of a sleeve-shaped refractory member is about 75 minutes,and a usable life of the sleeve-shaped refractory member is 150 to 250heats, and 200 heats on an average, at most. In a single converter usedin a typical steel plant, a tapping interval (tap-to-tap) is 40 minuteson an average, and about 12,000 heats of molten steel is refined for theyear. Given that a usable life of the sleeve-shaped refractory member is200 heats on an average, a replacement frequency (number of times ofreplacement) is 60 times/year. When an average time necessary for thereplacement is 75 minutes/replacement, an annul operation interruptiontime to be spent for the replacement runs up to about 4,500 minutes (75hours).

If the time necessary for the replacement of the sleeve-shapedrefractory member can be reduced to half, i.e., 37.5 minutes on anaverage, the annul operation interruption time to be spent for thereplacement will be reduced to half, i.e., about 2,250 minutes (37.5hours), and an operating time of the converter and a quantity ofproduction can be increased by just that much. Further, if the usablelife of the sleeve-shaped refractory member can be doubled, i.e., 400heats on an average, the replacement frequency will be reduced to half,i.e., 30 times/year. When the average time necessary for the replacementis 75 minutes/replacement, the annul operation interruption time to bespent for the replacement will also be reduced to half, i.e., about2,250 minutes (37.5 hours), and an operating time of the converter and aquantity of production can also be increased by just that much.

In reality, the sleeve-shaped refractory member is firmly bonded to arefractory lining of a converter using a castable refractory material,such as mortar, and a replacement operation has to be carried out in ahigh-temperature environment. Thus, there is an actual problem aboutextreme difficulty in further reducing the replacement time.

While it is contemplated to use the tundish nozzle replacing apparatusesdisclosed in the Patent Publications 2 and 3, in replacement of atapping sleeve of a converter, a heat resistance of these apparatuseswill emerge as a serious problem, because the converter is continuouslyoperated while handling molten steel which has a higher temperature thanthat in a tundish by about 50 to 100° C. Particularly, in the tundishnozzle replacing apparatuses, springs for pressing a tundish nozzle orimmersion nozzle (corresponding to the replaceable sleeve-shapedrefractory member) against an upper nozzle, and a hydraulic cylinder forslidingly moving the tundish nozzle or immersion nozzle in a horizontaldirection will be subjected to high temperatures to cause thermaldegradation. While a cooling device may be added to suppress thisproblem, a tilt or rotational movement of the converter will causeanother problem about structural complexity and increase in size of thecooling device.

In a sliding nozzle apparatus, the following Patent Publication 4discloses a technique of controllably opening and closing an nozzleopening using a plate brick with a hole having an excessively large holediameter to maintain an optimal flow volume so as to reduce an averagetapping time.

A converter has to handle molten steel which has a higher temperaturethan a ladle or tundish by about 50 to 100° C. and a flow volume 5 to 10times greater than that in the ladle or tundish. Thus, if the abovesliding nozzle apparatus for a ladle or tundish is used in a converter,a refractory component will have severe wear and have to be frequentlyreplaced due to shortened usable life thereof to cause a problem aboutdeterioration in operational efficiency, contrary to the intendedpurpose. Moreover, the above sliding nozzle apparatus is designed tonarrow a nozzle opening using a plurality of plate bricks so as tocontrol a flow volume. Thus, a molten steel flow to be dischargedbecomes turbulent to cause a problem about entrainment of air in themolten metal.

[Patent Publication 1] Japanese Patent Laid-Open Publication No.05-195038

[Patent Publication 2] Japanese Patent Laid-Open Publication No.200-1-150108

[Patent Publication 3] Japanese Patent Laid-Open Publication No.10-286658

[Patent Publication 4] Japanese Patent Publication No. 55-038007

DISCLOSURE OF THE INVENTION

It is an object of the present invention to find means for reducing anaverage discharging time in a molten metal vessel, such as a converter,having a molten-metal discharge nozzle particularly a molten-metaldischarge nozzle comprising a sleeve-shaped refractory member, so as toachieve enhanced operational efficiency of the molten metal vessel.

It is another object of the present invention to provide a molten-metaldischarge nozzle comprising a sleeve-shaped refractory member mounted ina molten metal vessel in a readily replaceable manner, and havingexcellent heat resistance and compactness.

It is yet another object of the present invention to provide a sleevereplacing apparatus capable of readily replacing the sleeve-shapedrefractory member of the discharge nozzle.

The inventors of this application assumed that an average dischargingtime may be reduced by using a conventional molten-metal dischargenozzle under the condition that an inner hole of a sleeve-shapedrefractory member has a relatively large cross-sectional area from aninitial stage of use.

While the use of a sleeve an inner hole having an initially largecross-sectional area causes a problem about increase in the frequency ofreplacement due to shortened usable life, this problem has been solvedby dividing the sleeve-shaped refractory member of the discharge nozzleinto two upper and lower sleeves, i.e., by frequently replacing only thelower sleeve. That is, the two-split structure allows the lower sleeveto be formed in a relatively small size having enhanced handleability soas to reduce a replacement time. Thus, it has been proven that theadvantage of reducing an average tapping time is fairly greater than thedisadvantage of increasing the replacement time. Reversely, the uppersleeve can be formed to have a relatively long usable life, and therebythe frequency of replacement for the upper sleeve will be advantageouslyreduced.

Further, a problem about heat resistance in an elastic member forpressing the lower sleeve is improved by associating the elastic memberwith the lower sleeve and replacing the elastic member every time thelower sleeve is replaced. Specifically, the lower sleeve is designed tobe held by a metal housing incorporating the elastic member to form anintegral unit.

Specifically, the present invention provides a discharge nozzle formolten metal in a molten metal vessel which comprises an upper sleeveand a lower sleeve adapted to be detachably attached to a lower end ofthe upper sleeve. Each of the upper and lower sleeves comprises arefractory member having an inner hole serving as a discharge passage ofmolten metal. This refractory member may be integrally formed as asingle piece, or may be an assembly of a plurality of refractorymembers. The upper sleeve is mounted to a refractory lining of themolten metal vessel, and made of a refractory material having a longerusable life than that of the lower sleeve. For example, the upper sleeveis made of a refractory material having a usable life approximatelyequal to or longer than that of the conventional sleeve-shapedrefractory member.

A flow volume of molten metal is controlled primarily by designing theinner hole of the lower sleeve to have a cross-sectional area providingan optimal molten-metal discharging time, and managing thecross-sectional area in a narrow range (a cross-sectional area of theinner hole of the upper or lower sleeve will hereinafter be referred toas “hole sectional area”). The frequency of replacement for the lowersleeve is 2 to 50 times greater than that for the upper sleeve. Thisfrequency of replacement is dependent on a time necessary forreplacement, and a usable life and/or cost of a refractory material tobe used therefor. If the replacement time is relatively short, the costof the refractory material is relatively low, the frequency ofreplacement can be increased to allow the average tapping time to becloser to an optimal value. In this case, the upper sleeve can be formedto have a longer useable life than the conventional sleeve-shapedrefractory member.

In the present invention, a hole sectional area of the upper sleeve inits newly-installed state, and a hole sectional area of the lower sleevein its newly-installed state, are determined on the basis of a holesectional area of the lower sleeve in its used state requiringreplacement. As used in this specification, the term “hole sectionalarea (i.e., cross-sectional area of the inner hole) of the lower sleevein its used state requiring replacement” means a hole sectional area ofthe lower sleeve, at a time when the lower sleeve is replaced with a newone after the inner hole of the lower sleeve is enlarged due to wearalong with increase in the number of heats, based on a user's oroperator's decision that the lower sleeve reaches the end of a usablelife thereof.

For example, in a steelmaking converter, if a given lower limit of atapping time is set up primarily for preventing entrainment of slag, thelower sleeve will be replaced with a new one when the tapping timereaches the given lower limit. The usable life of the lower sleeve maybe determined by a state, i.e., level, of entrainment of slag.

As used in this specification, the term “hole sectional area (i.e.,cross-sectional area of the inner hole)” means a cross-sectional area ina portion of the inner hole where a flow rate in each of the upper andlower sleeves is substantially regulated, i.e., a cross-sectional areain the narrowest portion of the inner hole in each of the upper andlower sleeves. Even if the inner hole partially has a stepped portion ora convex portion, the term “hole sectional area (i.e., cross-sectionalarea of the inner hole)” means a portion of the inner hole where a flowrate is substantially regulated, irrespective of such configurations.

In the present invention, the hole sectional area of the lower sleeve inthe newly-installed state is set preferably in the range of 60 to 98%,more preferably in the range of 67 to 97%, of the hole sectional area ofthe lower sleeve in the used state requiring replacement. If the holesectional area is less than 60%, a time required for discharging moltenmetal will be excessively increased, and the effect of reducing theaverage discharging time cannot be adequately obtained. If the holesectional area exceeds 98%, the frequency of replacement for the lowersleeve will be excessively increased to increase a time to be uselesslyspent for replacement and preclude an intended improvement inoperational efficiency of the molten metal vessel, such as a converter,from being obtained. The above term “newly-installed state” means astate at a time just after of the lower sleeve is newly installed in themolten metal vessel or replaced with a new one, i.e., an unused state.

As described, the flow volume is controlled primarily by the lowersleeve. Thus, the effects of the present invention can be obtainedwithout particularly restricting the hole sectional area of the uppersleeve. Thus, the number of usable times of the upper sleeve can bedrastically extended (increased). The reason is that, for example, evenif the hole sectional area of the upper sleeve in its newly-installedstate is less than the hole sectional area of the lower sleeve in itsnewly-installed state, the effect of the flow volume control of thelower sleeve becomes prominent as the number of times of use isincreased. In view of obtaining greater effect of the present invention,the hole sectional area of the upper sleeve in its newly-installed stateis preferably set in the range of 85 to 200% of the hole sectional areaof the lower sleeve in the used state requiring replacement. The holesectional area being less than 85% causes excessive increase inmolten-metal discharging time, and the hole sectional area exceeding200% causes poor handleability. More preferably, the lower sleeve may beused in such a manner that the hole sectional area of the lower sleevein the newly-installed state is set at a value less than the holesectional area of the upper sleeve. In this case, the average tappingtime can be further reduced.

In the present invention, the lower sleeve may be detachably attached tothe upper sleeve in such a manner that the lower sleeve is brought intopress contact with the upper sleeve by a reaction force of the elasticmember compressed when the metal housing is supported by a rail of aretention member fixed to the molten metal vessel, and moved along alongitudinal direction of the rail. The rail may have oppositelongitudinal ends each formed with an inclined surface adapted to relaxthe compression of the elastic member. Further, in view of facilitatingdetachable attachment of the lower sleeve to the lower end of the uppersleeve, the upper sleeve is preferably installed in the molten metalvessel in such a manner that the lower end of the upper sleeve protrudesfrom an outer surface of the molten metal vessel.

The present invention further provides a sleeve replacing apparatus forreplacing the lower sleeve with a new one. This sleeve replacingapparatus comprises a new-sleeve holding portion adapted to hold a newlower sleeve which is the lower sleeve in its unused state and before areplacement operation, a current-sleeve receiving portion adapted toreceive therein the lower sleeve which is currently in press contactwith the upper sleeve while being supported by the rail, an old-sleeveholding portion adapted to hold an old lower sleeve which is the lowersleeve in its used state and after the replacement operation, andarranged together with the new-sleeve holding portion and thecurrent-sleeve receiving portion in a linear manner, and an actuatoradapted to push out the new lower sleeve held by the new-sleeve holdingportion toward the current-sleeve receiving portion. The actuator isoperable to push out the new lower sleeve toward the current-sleevereceiving portion in such a manner that the new lower sleeve is broughtinto press contact with the upper sleeve while being supported by therail, so as to allow the lower sleeve which has been in press contactwith the upper sleeve to be pushed out and moved to the old-sleeveholding portion and held by the old-sleeve holding portion as an oldlower sleeve.

This sleeve replacing apparatus may be adapted to be moved while beingheld by a manipulator, and provided with a guide rod adapted to beinserted into a guide horn provided on the molten metal vessel. In thiscase, during the replacement operation, the guide rod is inserted intothe guide horn according to a manipulation of the manipulator, so as tofix a position of the sleeve replacing apparatus.

As above, according to the present invention, the discharging time ofmolten metal in the molten metal vessel can be minimized whilepreventing entrainment of contaminants, such as slag, and the dischargenozzle can be efficiently replaced to drastically improve operationalefficiency of the molten metal vessel.

Further, a problem about heat resistance in an elastic member forpressing the lower sleeve can be improved by associating the elasticmember with the lower sleeve and replacing the elastic member every timethe lower sleeve is replaced. This makes it possible to achieve enhancedheat resistance of the discharge nozzle in its entirety.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be specifically described based on anembodiment thereof where the present invention is applied to a tappingnozzle of a steelmaking converter.

FIG. 1 is a sectional view showing a tapping nozzle 31 of a converter ina state after the converter is tilted to allow an axis of the tappingnozzle 31 to extend vertically. The tapping nozzle 31 comprises an uppersleeve 32 mounted to a refractory lining of the converter, and a lowersleeve 33 adapted to be detachably attached to a lower end of the uppersleeve 32. Each of the upper and lower sleeves 32, 33 illustrated inFIG. 1 is a new product in an unused state.

The upper sleeve 32 comprises a cylindrical-shaped refractory member 34,and a plate-shaped refractory member 35 provided at a lower end thereofand formed with a nozzle hole. In the installed state, the lower end ofthe upper sleeve 32 protrudes from an outer surface 36 of the converter,and the upper sleeve 32 is fixed to a support brick 37 by mortar. Thelower sleeve 33 comprises a cylindrical-shaped refractory member 38, anda plate-shaped refractory member 39 provided at an upper end thereof andformed with a nozzle hole. The lower sleeve 33 is held by a lower-sleevereplacing apparatus 40 disposed along the lower end of the upper sleeve,and an upper end surface of the lower sleeve is in press contact with alower end surface of the upper sleeve. In FIG. 1, the lower-sleevereplacing apparatus 40 is fixed to a shell of the converter to hold thelower sleeve while pressing the lower sleeve against the upper sleeve byan elastic member (not shown). When the tapping nozzle 31 is repeatedlyused in this state, an inner diameter of an inner hole of the lowersleeve will be gradually increased, and the lower sleeve will finallyreach the end of its usable life. In this embodiment, an inner diameterof an inner hole of the upper sleeve in its newly-installed state isdesigned to be 88% of an inner diameter of the inner hole of the lowersleeve in its used state requiring replacement.

As shown in FIG. 2, the lower sleeve 33 which has reached the end of theusable life is replaced with a new lower sleeve 41. An immersion-nozzlereplacing apparatus disclosed in Japanese Patent Laid-Open PublicationNo. 2002-346705 is used as the replacing apparatus for this replacementoperation. Specifically, the new lower sleeve 41 is pushed in ahorizontal direction by a drive device, such as a hydraulic cylinder, sothat the old lower sleeve 33 is pushed out and replaced with the newlower sleeve 41. More specifically, the replacing apparatus comprises aretaining metal frame fixed to a side surface of the converter andadapted to receive therein the upper sleeve, a pair of spring members(not shown) disposed in opposed relation to each other on both sides ofthe upper sleeve having a sliding surface, a plurality of latch plates(not shown) associated with a spring member and biased upwardly, and aguide rail. In this apparatus, a pusher for pushing the new lower sleeveand a drive source thereof are detachably attached to the converter,instead of being fixed to the converter.

Table 1 and FIG. 3 show an operation of the converter using thesleeve-type tapping nozzle illustrated in FIG. 1. TABLE 1 ComparativeInventive Example 1 Example 1 Hole sectional area of lower sleeve after100 use (%) Hole sectional area of upper sleeve in newly- 100 installedstate (%) Hole sectional area of lower sleeve in newly- 88 installedstate (%) Hole sectional area of sleeve in used state 100 requiringreplacement (%) Hole sectional area of conventional sleeve in 50newly-installed state (%) Tapping time in initial stage of use(min/heat) 10.0 6.3 Tapping time in last stage of use (min/heat) 5.0 5.0Average tapping time (min/heat) 7.50 5.63 Reduction in tapping timerelative to 1.87 Comparative Example 1 (min/heat) Effect of reduction ofaverage tapping time 374 (min/200 heats) Usable life of lower sleeve(heat) 50.0 Frequency of replacement for lower sleeve 4 Totallower-sleeve replacement time 80 (min/200 heats) Improvement ofoperational efficiency 294 (min/200 heats)

In Comparative Example 1 and Inventive Example 1 shown in Table 1, ahole sectional area of the lower sleeve after use was obtained bymeasuring respective hole sectional areas of four lower sleeves afteruse, and calculating an average of the measured hole sectional areas.Specifically, the calculated average was 707 cm² (inner diameter: 300mm), and this value was used as a reference hole sectional area of thelower sleeve in the used state requiring replacement, or defined as100%. A hole sectional area of the upper sleeve in the newly-installedstate was set at the same value as the hole sectional area of the lowersleeve in the used state requiring replacement. A hole sectional area ofthe lower sleeve in the newly-installed state was 88% of the holesectional area of the lower sleeve after use. The number of tappings wasset at 200. The average tapping time in Table 1 indicates an average of200 tapping times. A length of the upper sleeve was set at 700 mm, and alength of the lower sleeve was set at 300 mm. Each of Inventive Example1 and Comparative Example 1 was made of a magnesia-carbon refractorymaterial.

FIG. 4 shows the structure of Comparative Example 1 as a conventionaltapping nozzle. The tapping nozzle of Comparative Example 1 was formedof a single sleeve-shaped refractory member 51 with an inner hole havingan approximately constant cross-sectional area, and installed in thesame converter as that in Inventive Example 1. This sleeve-shapedrefractory member had a hole sectional area of 707 cm² (inner diameter:300 mm) after being used 200 times, i.e., in the used state requiringreplacement, and an initial hole sectional area was 50% of the holesectional area after use.

As shown in FIG. 5, Comparative Example 1 has a relatively long tappingtime of 10 minutes in an initial stage of use because of its initialhole sectional area of 50%, and the tapping time is gradually reducedalong with increase in the number of times of use. As the result,Comparative Example 1 had an average tapping time of 7.5 minutes. Incontrast, as shown in FIG. 3, Inventive Example 1 has a relatively shorttapping time of 6.25 in an initial stage of use because of an initialhole sectional area of 88% which is greater than that of ComparativeExample 1. Thus, Inventive Example 1 had an average tapping time of 5.63minutes which is shorter than that of Comparative Example 1 by 1.87minutes as shown in Table 1. The lower sleeve has to be replaced every50 heats, and the average replacement time is 20 minutes. That is, thelower sleeve has to be replaced 4 times during a period of 200 heats,and therefore a total replacement time is 80 minutes. Thus, when thetapping is performed 200 times in this converter, an advantage of 1.87min/tapping×200 tappings−80 min=294 minutes can be obtained asimprovement of operational efficiency.

This converter is operated at 12000 heats a year. Thus, an advantageoustime is 294 hours for a year. If this time is used for refining, aquantity of production will be increased by 442.5 heats/year or 132,750ton/year.

Table 2 shows the result on improvement of operational efficiencycalculated by variously changing the hole sectional area of the lowersleeve in the newly-installed state and the lower-sleeve replacementtime in the above example. TABLE 2 Comparative Comparative InventiveInventive Inventive Inventive Inventive Example 1 Example 2 Example 2Example 3 Example 4 Example 5 Example 6 Hole sectional area of lowersleeve after use (%) 100 100 100 100 100 100 Hole sectional area ofupper sleeve in newly-installed 100 100 100 100 100 100 state (%) Holesectional area of lower sleeve in newly-installed 99 98 97 94 88 67state (%) Hole sectional area of sleeve in used state requiring 100replacement (%) Hole sectional area of conventional sleeve in newly- 50installed state (%) Tapping time in initial stage of use (min/heat) 10.05.1 5.2 5.3 5.6 6.3 8.3 Tapping time in last stage of use (min/heat) 5.05.0 5.0 5.0 5.0 5.0 5.0 Average tapping time (min/heat) 7.5 5.0 5.1 5.25.3 5.6 6.7 Reduction in average tapping time relative to 2.46 2.42 2.342.19 1.88 0.83 Comparative Example 1 (min/heat) Reduced time in averagetapping time relative to 492 484 469 438 375 167 Comparative Example 1(hour/year) (1) Usable life of lower sleeve (heat) 0 3.1 6.3 12.5 25.050.0 133.3 Replacement time of lower sleeve (min/tapping) 5 5 5 5 5 5Replacement time of lower sleeve (2) (hour/year) 320 160 80 40 20 8Improved time in operational efficiency (1) − 172 324 389 398 355 159(2) (hour/year) Replacement time of lower sleeve (min/tapping) 10 10 1010 10 10 Replacement time of lower sleeve (3) (hour/year) 640 320 160 8040 15 Improved time in operational efficiency (1) − −148 164 309 358 335152 (3) (hour/year) Replacement time of lower sleeve (min/tapping) 20 2020 20 20 20 Replacement time of lower sleeve (4) (hour/year) 1280 640320 160 80 30 Improved time in operational efficiency (1) − −788 −156149 278 295 137 (4) (hour/year)(Note)Replacement time of lower sleeve (hour/year) was calculated by thefollowing formula: (12000/usable life of lower sleeve) × replacementtime of lower sleeve

The above calculation was performed on the assumption that the converteris operated at 12000 tappings a year. Further, a wear rate was set atthe same value as that in Inventive Example 1. As seen in Table 2, theimprovement of operational efficiency becomes larger as the lower-sleevereplacement time is shorter. When the replacement time is 5 minutes, allInventive Examples 2 to 6 and Comparative Example 1 can get goodresults. When the replacement time is 10 minutes, no advantage isobtained if the hole sectional area is equal to or greater than 98% ofthe hole sectional area of the lower sleeve after use. This result showsthat the hole sectional area of the lower sleeve in the newly-installedstate is more preferably in the range of 97 to 67% in consideration ofsome margin in replacement time. A lower-sleeve replacement time of 20minutes can be surely achieved by a conventional technique, e.g., atechnique for a continuous casting nozzle, of fixing the lower sleeveusing a bayonet, bolt or the like.

FIG. 6 is an exploded perspective view showing a molten-metal dischargenozzle and a sleeve replacing apparatus, according to a secondembodiment of the present invention, and FIG. 7 is a perspective viewshowing an upper portion of the molten-metal discharge nozzle in FIG. 6.

The molten-metal discharge nozzle illustrated in FIGS. 6 and 7 comprisesan upper sleeve 2 mounted to a refractory lining of a converter 1, and alower sleeve 3 adapted to be detachably attached to an distal end of theupper sleeve 2. FIGS. 6 and 7 show only a part of the converter,specifically, a vicinity of a tapping port of the converter.

FIG. 8(a) is a top plan view showing the lower sleeve 3. FIG. 8(b) is asectional view taken along the line A-A in FIG. 8(a), and FIG. 8(c) is asectional view taken along the line B-B in FIG. 8(a). As shown in FIGS.8(a) to 8(c), the lower sleeve 3 is mounted to a metal housing 4comprising an outer metal frame 4 a and an inner metal frame 4 b. Asshown in FIG. 8(c), an elastic member 5 composed of a coil spring isembedded in a space between the outer metal frame 4 a and the innermetal frame 4 b, so that the outer metal frame 4 a holds the inner metalframe 4 b through the elastic member 5 in a vertically movable manner.Specifically, the elastic member 5 is fit on a guide protrusion 6extending downwardly from a lower surface of the inner metal frame 4 b,so as to be kept from moving laterally. As shown in FIG. 8(b), a guidepin 7 is provided as a means to guide the vertical movement of the innermetal frame 4 b. The guide protrusion 6 has a length set to avoidconflict with the outer metal frame 4 a even when the elastic member 5is maximally compressed. In this embodiment, a total of the ten guideprotrusions 6 are arranged in a concentric pattern. Further, the outermetal frame 4 a is provided with a cooling horn 8 serving as an ambientair inlet for introducing ambient air to the elastic member 5 to coolthe elastic member 5.

The inner metal frame 4 b has a lateral surface provided with a sleevelock device 9 for locking the lower sleeve 3. The sleeve lock device 9comprises a screw mechanism and a sleeve pressing plate 9 a attached atdistal end of the screw mechanism. According to the screw mechanism, thesleeve pressing plate 9 a is moved inwardly and pressed against alateral surface of the lower sleeve 3 to lock the lower sleeve 3 to theinner metal frame 4 b.

The lower sleeve 3 is made of a refractory material, and an uppersurface of the lower sleeve 3 is formed as a contact surface 3 a withthe upper sleeve 2. The contact surface 3 a has a generally circularshape, and an outer periphery of the contact surface 3 a includes a pairof parallel edges 3 b. Each of the parallel edges 3 b is formed toextend in a direction orthogonal to a moving direction of the lowersleeve during an after-mentioned replacement operation. Further, each ofthe parallel edges 3 b is formed to have a length greater than adiameter of the inner hole 3 c so as to prevent the lower sleeve 3 frombeing damaged due to a pushing force during the replacement operation.If the contact surface 3 a is formed in a perfect circle without theparallel edges 3 b, the contact surface 3 a will come into point contactwith the inner metal frame 4 a during the replacement operation, andresulting stress concentration is likely to damage the contact surface 3a. Further, if the length of each of the parallel edges 3 b is less thanthe inner hole 3 c, a crack occurring from the parallel edges 3 b islikely to penetrate through the inner hole 3 c.

In this embodiment, the lower sleeve 3 is a single-piece product.Alternatively, the lower sleeve 3 may be a multi-part product formed,for example, by preparing an upper portion including the contact surface3 a and a cylindrical-shaped lower portion separately, and joining themtogether. Further, an outer surface of the lower sleeve 3 may be coveredby a metal case to effectively prevent damages.

FIG. 9 is a fragmentary sectional view showing the upper sleeve 2. Asshown in FIG. 9, the upper sleeve 2 is mounted to a metal housing 10comprising an outer metal frame 10 a and an inner metal frame 10 b. Theouter metal frame 10 a is fixed to a base plate 11 secured to theconverter 1, and the inner metal frame 10 b is attached to the outermetal frame 10 a by a pin 12 in a vertically movable manner. The innermetal frame 10 b has a lateral surface provided with a sleeve lockdevice 13 for locking the upper sleeve 2. The sleeve lock device 13 hasthe same structure as that of the aforementioned sleeve lock device 9for locking the lower sleeve 2, and its description will be omitted.

The upper sleeve 2 is made of a refractory material as with the lowersleeve, and a lower surface of the upper sleeve 2 is formed as a contactsurface 2 a with the lower sleeve 3. As shown in FIG. 7, the contactsurface 2 a has a generally circular shape, and an outer periphery ofthe contact surface 2 a includes a pair of parallel edges 2 b. Each ofthe parallel edges 2 b is formed to extend in a direction orthogonal toa moving direction of the lower sleeve during the after-mentionedreplacement operation. Further, each of the parallel edges 2 b is formedto have a length greater than a diameter of an inner hole 2 c of theupper sleeve 2.

The upper sleeve 2 is fixed to the refractory lining of the converter 1through a castable refractory material filled therebetween.

FIG. 10 is a fragmentary sectional view showing the lower sleeve 3 afterbeing brought into press contact with the lower end of the upper sleeve2. A pair of retention members 14 are fixed to the base plate 11 andprovided with a rail 14 a, and the lower sleeve 3 is held by the rail 14a. In this retention state, the outer metal frame 4 a of the metalhousing 4 which holds the lower sleeve 3 is pushed upwardly, i.e.,lifted, to compress the elastic member 5. Then, according to a reactionforce of the elastic member 5, the inner metal frame 4 a is liftedtogether with the lower sleeve 3, and the contact surface 3 a of thelower sleeve 3 is reliably brought into press contact with the contactsurface 2 a of the upper-sleeve 2.

As above, the metal housing 4 which holds the lower sleeve 3 can beslidingly moved along a longitudinal direction of the rail 14 a. Thus,an operation of replacing the lower sleeve 3 with a new one can beperformed by slidingly moving the metal housing 4 (lower sleeve 3) alongthe longitudinal direction of the rail 14 a. In this embodiment, a liner26 is provided on the lower surface of the outer metal frame 4 a of themetal housing 4 and each surface of the rail 14 a to facilitate thesliding movement and provide enhanced frictional resistance.

Further, as shown in FIG. 7, the rail 14 a has opposite lateral endseach formed with an inclined surface 14 b. This inclined surface 14 b isformed to extend downwardly toward each end edge of the rail 14 b. Thus,when the metal housing 4 (lower sleeve 3) is slidingly moved along thelongitudinal direction of the rail 14 a, a lift amount of the outermetal frame 4 a of the metal housing 4 is reduced in these regionshaving the inclined surface 14 b, and thereby the compression of theelastic member 5 is relaxed to reduce a pressing force of the lowersleeve 3 against the upper sleeve 2. This makes it possible to smoothlyperform the replacement operation for the lower sleeve 3.

The sleeve replacing apparatus according to the second embodiment of thepresent invention will be described below.

As shown in FIG. 6, the sleeve replacing apparatus 15 comprises anew-sleeve holding portion 16 adapted to hold a new lower sleeve whichis the lower sleeve 3 in the unused state and before the replacementoperation, a current-sleeve receiving portion 17 adapted to receivetherein the lower sleeve 3 which is currently in press contact with theupper sleeve, an old-sleeve holding portion 18 adapted to hold an oldlower sleeve which is the lower sleeve 3 in the used state and after thereplacement operation, and a base 19. The new-sleeve holding portion 16,the current-sleeve receiving portion 17 and the old-sleeve holdingportion 18 are arranged on the base 19 in a linear manner in this order.Each of the new-sleeve holding portion 16 and the old-sleeve holdingportion 18 is formed with a guide rail (16 a, 18 a) adapted to slidablysupport the metal housing for each of the new lower sleeve and the oldlower sleeve. The sleeve replacing apparatus 15 further includes anactuator 20 composed of a hydraulic cylinder and disposed on the side ofthe new-sleeve holding portion 16.

As shown in FIGS. 6 and 7, a pair of positioning guide horns 21 arefixed to the base plate of the converter 1 and disposed to allow acenter of a diagonal line connecting between the guide horns 21 to belocated at a center of the inner hole 2 c, and a pair of guide rods 22are fixed on the base 19 of the sleeve replacing apparatus 15 atrespective positions corresponding to the guide horns 21.

A lower-sleeve replacement operation using the sleeve replacingapparatus 15 will be described below.

FIGS. 11(a) and 11(b) are explanatory views of the lower-sleevereplacement operation using the sleeve replacing apparatus, whereinFIGS. 11(a) and 11(b) are a top plan view and a side view of the sleevereplacing apparatus. FIG. 12 is a fragmentary sectional view showing thesleeve replacing apparatus during the lower-sleeve replacementoperation.

In advance of the lower-sleeve replacement operation, a new lower sleeve3′ is slidingly attached to the guide rail 16 a and held by thenew-sleeve holding portion 16 of the sleeve replacing apparatus 15 (seeFIG. 12). Then, as shown in FIGS. 11(a) and 11(b), the sleeve replacingapparatus 15 is held by a manipulator 24 on a movable dolly 23, and thedolly 23 is moved along a track 25 to allow the sleeve replacingapparatus 15 to come close to the converter 1. Then, the manipulator 24is manipulated to insert the guide rods 22 of the sleeve replacingapparatus 15 into the corresponding guide horns 21 while adjustingvertical and horizontal positions of the sleeve replacing apparatus 15so as to fix a position of the sleeve replacing apparatus 15.

Referring to FIG. 12 to describe a subsequent process, the actuator 20of the sleeve replacing apparatus 15 is driven forward (extended) topush out the new lower sleeve 3′ held by the new-sleeve holding portion16, toward the current-sleeve receiving portion 17. Through thisoperation, the new lower sleeve 3′ is ridden on the rail 14 a andbrought into press contact with the upper sleeve 2, as shown in FIG. 10,to allow a lower sleeve 3″ (see FIG. 12) which has been in press contactwith the upper sleeve to be pushed out and slidingly moved to theold-sleeve holding portion 18 along the guide rail 18 a and held by theold-sleeve holding portion 18 as an old lower sleeve. Through the aboveprocess, the lower-sleeve replacement operation is completed.

A discharge nozzle having the structure according to this embodiment wasapplied to an actual concreter, and a lower-sleeve replacement operationwas carried out using the sleeve replacing apparatus. As the result, thereplacement operation could be completed within 5 minutes.

INDUSTRIAL APPLICABILITY

The present invention can be applied to not only steelmaking convertersbut also nonferrous-metal refining converters and other tilt furnaces.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing a molten-metal dischargenozzle according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a lower sleeve of themolten-metal discharge nozzle during a replacement operation.

FIG. 3 is a graph showing a replacement operation for a lower sleeve ofa molten-metal discharge nozzle as Inventive Example 1.

FIG. 4 is a schematic sectional view showing a molten-metal dischargenozzle as Comparative Example 1.

FIG. 5 is a graph showing an operation of replacing a lower sleeve ofComparative Example 1.

FIG. 6 is a fragmentary exploded perspective view showing a sleevereplacing apparatus and a molten-metal discharge nozzle, according to asecond embodiment of the present invention.

FIG. 7 is a fragmentary perspective view showing an upper portion of themolten-metal discharge nozzle in FIG. 6.

FIGS. 8(a) to 8(c) show a lower sleeve of the molten-metal dischargenozzle in FIG. 6, wherein FIGS. 8(a), 8(b) and 8(c) are a top plan view,a sectional view taken along the line A-A in FIG. 8(a) and a sectionalview taken along the line B-B in FIG. 8(a), respectively.

FIG. 9 is a fragmentary sectional view showing an upper sleeve of themolten-metal discharge nozzle in FIG. 6.

FIG. 10 is a fragmentary sectional view showing the upper sleeve and thelower sleeve in the molten-metal discharge nozzle in FIG. 6, wherein thelower sleeve is in press contact with the upper sleeve.

FIGS. 11(a) and 11(b) are explanatory views of the lower-sleevereplacement operation using the sleeve replacing apparatus, whereinFIGS. 11(a) and 11(b) are a top plan view and a side view of the sleevereplacing apparatus.

FIG. 12 is a fragmentary sectional view showing the sleeve replacingapparatus during the lower-sleeve replacement operation.

DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS

-   1 converter-   2 upper sleeve-   2 a contact surface-   2 b parallel edge-   2 c inner hole-   3 lower sleeve-   3′ new lower sleeve-   3″ old lower sleeve-   3 a contact surface-   3 b parallel edge-   3 c inner hole-   4 metal housing-   4 a outer metal frame-   4 b inner metal frame-   5 elastic member-   6 guide protrusion-   7 guide pin-   8 cooling horn (ambient air inlet)-   9 sleeve lock device-   9 a sleeve pressing plate-   10 metal housing-   10 a outer metal frame-   10 b inner metal frame-   11 base plate-   12 pin-   13 sleeve lock device-   14 retention member-   14 a rail-   14 b inclined surface-   15 sleeve replacing apparatus-   16 new-sleeve holding portion-   16 a guide rail-   17 current-sleeve receiving portion-   18 old-sleeve holding portion-   18 a guide rail-   19 base-   20 actuator-   21 guide horn-   22 guide rod-   23 movable dolly-   24 manipulator-   25 track-   26 liner-   31 tapping nozzle-   32 upper sleeve-   33 lower sleeve-   34, 38 cylindrical-shaped refractory member-   35, 39 plate-shaped refractory member-   36 outer surface of converter-   37 support brick-   40 lower-sleeve replacing apparatus-   41 new lower sleeve-   51 sleeve-shaped refractory member

1. A discharge nozzle for molten metal in a molten metal vessel,comprising an upper sleeve and a lower sleeve adapted to be detachablyattached to a lower end of said upper sleeve, wherein said lower sleeveis formed with an inner hole in such a manner that a cross-sectionalarea of the inner hole of said lower sleeve in its newly-installed stateis in the range of 60 to 98% of a cross-sectional area of the inner holeof said lower sleeve in its used state requiring replacement.
 2. Thedischarge nozzle as defined in claim 1, wherein said upper sleeve isformed with an inner hole in such a manner that a cross-sectional areaof the inner hole of said upper sleeve in its newly-installed state isin the range of 85 to 200% of the cross-sectional area of the inner holeof said lower sleeve in said used state requiring replacement.
 3. Thedischarge nozzle as defined in claim 1, wherein said upper sleeve isadapted to be installed in said molten metal vessel in such a mannerthat the lower end of said upper sleeve protrudes from an outer surfaceof said molten metal vessel.
 4. A discharge nozzle for molten metal in amolten metal vessel, comprising: an upper sleeve; and a lower sleeveadapted to be detachably attached to a lower end of said upper sleeve,in such a manner that said lower sleeve is associated with an elasticmember for allowing said lower sleeve to be brought into press contactwith said upper sleeve, and held by a metal housing incorporating saidelastic member to form an integral unit, wherein said lower sleeve isbrought into press contact with said upper sleeve by a reaction force ofsaid elastic member compressed when said metal housing is supported by arail of a retention member fixed to said molten metal vessel, andallowed to be detached from said upper sleeve when moved along alongitudinal direction of said rail.
 5. The discharge nozzle as definedin claim 4, wherein said metal housing has an ambient-air inlet forintroducing ambient air to said elastic member.
 6. The discharge nozzleas defined in claim 4, wherein said rail has opposite longitudinal endseach formed with an inclined surface adapted to relax the compression ofsaid elastic member.
 7. The discharge nozzle as defined in claim 4,wherein each of said upper sleeve and said lower sleeve is formed tohave a generally circular-shaped contact surface therebetween, and aninner hole having an axis aligned with a center of said contact surface,said contact surface having an outer periphery which includes a pair ofparallel edges each extending in a direction orthogonal to said movingdirection of said lower sleeve during the detachment and having a lengthgreater than an inner diameter of said nozzle hole.
 8. The dischargenozzle as defined in claim 4, wherein a cross-sectional area of theinner hole of said lower sleeve in its newly-installed state is in therange of 60 to 98% of a cross-sectional area of the inner hole of saidlower sleeve in its used state requiring replacement.
 9. The dischargenozzle as defined in claim 8, wherein a cross-sectional area of theinner hole of said upper sleeve in its newly-installed state is in therange of 85 to 200% of the cross-sectional area of the inner hole ofsaid lower sleeve in said used state requiring replacement.
 10. Thedischarge nozzle as defined in claim 8, wherein said upper sleeve isadapted to be installed in said molten metal vessel in such a mannerthat the lower end of said upper sleeve protrudes from an outer surfaceof said molten metal vessel.
 11. A sleeve replacing apparatus for thedischarge nozzle as defined in claim 4, comprising: a new-sleeve holdingportion adapted to hold a new lower sleeve which is the lower sleeve inits unused state and before a replacement operation; a current-sleevereceiving portion adapted to receive therein the lower sleeve which iscurrently in press contact with said upper sleeve while being supportedby said rail; an old-sleeve holding portion adapted to hold an old lowersleeve which is the lower sleeve in its used state and after saidreplacement operation, and arranged together with said new-sleeveholding portion and said current-sleeve receiving portion in a linearmanner; and an actuator adapted to push out said new lower sleeve heldby said new-sleeve holding portion toward said current-sleeve receivingportion, said actuator being operable to push out said new lower sleevetoward said current-sleeve receiving portion in such a manner that saidnew lower sleeve is brought into press contact with said upper sleevewhile being supported by said rail, so as to allow said lower sleevewhich has been in press contact with said upper sleeve to be pushed outand moved to said old-sleeve holding portion and held by said old-sleeveholding portion as an old lower sleeve.
 12. The sleeve replacingapparatus as defined in claim 11, which is adapted to be moved whilebeing held by a manipulator, and provided with a guide rod adapted to beinserted into a guide horn provided on the molten metal vessel, wherein,during said replacement operation, said guide rod is inserted into theguide horn according to a manipulation of said manipulator, so as to fixa position of the sleeve replacing apparatus.
 13. A method for operationof a converter having a molten-metal discharge nozzle which includes anupper sleeve and a lower sleeve detachably attached to a lower end ofsaid upper sleeve, comprising: allowing said lower sleeve to have aninner hole formed such that a cross-sectional area of the inner hole ofsaid lower sleeve in its newly-installed state is in the range of 60 to98% of a cross-sectional area of the inner hole of said lower sleeve inits used state requiring replacement; and operating said converter underthe condition that the cross-sectional area of the inner hole of saidlower sleeve is maintained at a value equal to or less than across-sectional area of an inner hole formed in said lower sleeve. 14.The method as defined in claim 13, which includes operating saidconverter under the condition that a cross-sectional area of the innerhole of said upper sleeve at a time when said lower sleeve is replacedand newly installed is maintained in the range of 85 to 200% of thecross-sectional area of the inner hole of said lower sleeve in said usedstate requiring replacement.